This invention relates to constructed wetlands that are used to treat wastewater, more particularly, for the control of the water level of such wetlands.
Constructed wetlands are artificial wastewater treatment systems consisting of shallow (usually less than 1 m deep) ponds or channels which have been planted with aquatic plants, and which rely upon natural microbial, biological, physical and chemical processes to treat wastewater. They typically have impervious clay or synthetic liners, and engineered structures to control the flow direction, liquid detention time and water level. Depending on the type of system, they may or may not contain an inert porous media such as rock, gravel or sand.
Constructed wetlands have been used to treat a variety of sources of wastewater including urban runoff, municipal, industrial, agricultural and acid mine drainage. While some degree of pre- or post-treatment may be required in conjunction with the wetland to treat wastewater to meet stream discharge or reuse requirements, the wetland will be the central treatment component.
For some applications, wetlands are an excellent option because they are low in cost and in maintenance requirements, offer good performance, and provide a natural appearance, if not more beneficial ecological benefits. However, because they require large land areas, 4 to 25 acres per million gallons of flow per day, wetlands are not appropriate for some applications. Constructed wetlands are especially well suited for wastewater treatment in small communities where inexpensive land is available and skilled operators are hard to find.
Constructed wetlands have been classified by the literature and practitioners into two types. Free water surface (FWS) wetlands (also known as surface flow wetlands) closely resemble natural wetlands in appearance because they contain aquatic plants that are rooted in a soil layer on the bottom of the wetland and water flows through the leaves and stems of plants. Vegetated submerged bed (VSB) systems (also known as subsurface flow wetlands) do not resemble natural wetlands because they have no standing water. They contain a bed of media (such as crushed rock, small stones, gravel, sand or soil) which has been planted with aquatic plants. When properly designed and operated, wastewater stays beneath the surface of the media, flows in contact with the roots and rhizomes of the plants, and is not visible or available to wildlife.
The term xe2x80x9cvegetated submerged bedxe2x80x9d is used herein instead of subsurface flow wetland because it is a more accurate and descriptive term. Some VSBs may meet the strict definition of a wetland, but a VSB does not support aquatic wildlife because the water level stays below the surface of the media, and is not conducive to many of the biological and chemical interactions that occur in the water and sediments of a wetland with an open water column. VSBs have historically been characterized as constructed wetlands in the literature, and so they are included in this application.
Constructed wetlands were first developed in the relatively warm climate of Tennessee. As use of these constructed wetlands spread northwards, concerns arose over the possibility of the wetlands freezing thereby disabling the water treatment system. The largest concern is that the level control system will freeze thereby flooding the wetland. Solutions that have been tried to maintain the function of a wetland during cold temperatures include massive amounts of insulation and/or provision of heating elements to maintain the temperature of the level control device. Grove et al. (U.S. Pat. No. 5,951,866) discloses a cold climate wetland wastewater treatment system in which the hydraulic level control structure is positioned entirely within the rear end of the containment area. These solutions add to the expense of the wetlands wastewater treatment system and the inconvenience of servicing the wetlands.
Therefore, it would be desirable to have a wetlands level control device that solves the aforementioned problems.
The present invention provides an improved level control device for wetland wastewater treatment facilities that overcomes the aforementioned problems. The device comprising: an outer casing with an open top, the outer casing having an inner diameter at least about 4 inches and less than about 18 inches; an overflow weir in fluid communication with the constructed wetlands, wherein the overflow weir is located within the outer casing; a cap removably attached in a closing position over the open top of the outer casing; and an outlet in fluid communication with the overflow weir wherein the outlet provides a fluid flow path through the outer casing.
An improved device for controlling the level of a constructed wetlands wastewater treatment system, the device comprising: an outer casing with an open top, the outer casing having an outer surface and an inner surface and an inner diameter at least about 4 inches and less than about 18 inches; an overflow weir comprising an overflow pipe in fluid communication with the constructed wetlands, wherein the overflow pipe is located within the outer casing and has an outer diameter at least about 2 inches less than the inner diameter of the outer casing; a cap removably attached in a closing position over the open top of the outer casing; and an outlet in fluid communication with the overflow weir wherein the outlet extends through the outer casing from the inner surface to the outer surface providing a fluid flow path through the outer casing.